The present invention relates to an inverter device and a motor driving device, and more particularly to an inverter device and motor driving device provided with an inrush current prevention circuit.
The conventional first type of inverter device includes a smoothing circuit for smoothing a power supply for a main circuit, an inrush current prevention circuit for preventing an inrush current from flowing into the smoothing circuit when the power supply for the main circuit is turned on and an inverter section which receives the current from the smoothing circuit, the inrush current prevention circuit being a relay or an electromagnetic contactor.
Moreover, a recent second type of inverter device with a small output power includes a smoothing circuit for smoothing a waveform of a power supply for a main circuit, an inrush current prevention circuit for preventing an inrush current from flowing into the smoothing circuit when the power supply for the main circuit is turned on, and an inverter section which receives a signal from the smoothing circuit, the inrush prevention circuit being a semiconductor element such as a thyristor. This inverter device uses a semiconductor module integrally composed of converters on the input and the output sides and a thyristor in the inrush prevention circuit.
In turn, the description will be oriented to the inrush prevention circuit used for this inverter device. In FIG. 1, a reference number 1 denotes an AC power supply. A reference number 2 denotes a rectifying circuit composed of a diode connected in a three-phase bridge. A reference number 7 denotes a smoothing circuit. A reference number 8 denotes an inverter section. A reference number 9 denotes a motor. A reference number 20 denotes circuit.
The AC power supply 1 is a commercial power supply and serves to supply a three-phase AC power. The rectifying circuit 2 serves to convert a three-phase AC power supplied from the AC power supply into direct current. The circuit 2 composes a DC power-supply for a main circuit.
The inrush current prevention circuit 20 serves to prevent the inrush current from flowing into the smoothing circuit 7 when the power supply is turned on and is located between the rectifying circuit 2 and the smoothing circuit 7. The smoothing circuit 7, composed of a smoothing capacitor, serves to smooth the DC voltage outputted from the rectifying circuit 2 and then to supply the smoothed voltage into the inverter section 8. The inverter section 8 is connected to semiconductor switching elements such as IGBTs connected in a three-phase bridge so that those semiconductor switching elements may be turned on and off by a control circuit (not shown) for driving the motor 9. This motor 9 is a three-phase inductive motor.
In the inrush current prevention circuit 20, a reference number 3 denotes a current-limiting resistor. A reference number 4 denotes a thyristor. A reference number 6 denotes a control unit for the inrush current prevention circuit. A reference number 10a denotes a resistor between an anode and a gate. A reference number 10b denotes a resistor between a gate and a cathode. A reference number 11 denotes a gate resistor for a photo thyristor. A reference number 12 denotes a photo thyristor. A reference number 15 denotes a power supply for the control unit for the inrush current prevention circuit. The thyristor 4 is independent and is connected in parallel to the current-limiting resistor 3. The photo thyristor 12 is located between the resistor 10a and the gate of the thyristor 4. The gate of the thyristor 4 is connected to a junction between the cathode of the photo thyristor 12 and the resistor 10b. 
The inverter device concerned with the prior art is described in JP-A-3-3668, for example.
The first type of Prior Art inverter device has a disadvantage in that its characteristics are varied according to the input frequency because coils are used for the relay of the inrush current prevention circuit and the electromagnetic contactor. For example, a constraint is placed on the receiving voltage of the inverter. Because of the use of a mechanical contact, the life of the contactor is limited. Further, the production of the mechanical contact is very costly.
The second type of Prior Art inverter device uses a single semiconductor switching element for the inrush current prevention circuit and is disadvantageous because of the capacitance and the endurance of the semiconductor switching element.
The high-power thyristor with a current capacity greater than 1000 A is mainly made as a pressure type device, while the semiconductor switching element of the 1000 A class of the IGBT (Insulated Gate Bipolar Transistor) often used as the semiconductor switching element of the inverter section is mainly made as a module type. This module type IGBT semiconductor switching element is mounted on a cooling fan. Hence, if the thyristor of the inrush current prevention circuit is located in the same box as the semiconductor switching element of the inverter section, the module type thyristor is more convenient. However, the maximum current of the module type thyristor is limited to about 400 A because of the yield-rate of the chips and so on.
It is an object of the present invention to provide an inverter device and a motor driving device which may be arranged to apply a semiconductor switching element to the an inrush current prevention circuit of the inverter device with a large capacitance and may be made inexpensively and highly reliably.
In carrying out the object, according to a first aspect of the invention, an inverter device includes a smoothing circuit for smoothing current of a power supply for a main circuit, an inrush current prevention circuit for preventing an inrush current from flowing into the smoothing circuit when the power supply for the main circuit is turned on, and an inverter section which receives a signal from the smoothing circuit and drives the motor. The inrush current prevention circuit includes current-limiter for limiting the inrush current, a plurality of semiconductor switching elements, and a driving circuit for the inrush current prevention circuit for driving these semiconductor switching elements. The semiconductor switching elements are connected in parallel to each other.
According to a second aspect of the invention, the plurality of semiconductor switching elements of the inrush current prevention circuit are connected in series with each other.
According to a third aspect of the invention, some of the semiconductor switching elements of the inrush current prevention circuit are connected in series with each other, and some combinations of the switching element circuits connected in series are in turn connected in parallel.
According to a fourth aspect of the invention, some of the semiconductor switching elements of the inrush current prevention circuit are connected in parallel with each other, and some parallel connections of the switching element circuits are in turn connected in series.
According to a fifth aspect of the invention, the driving circuit for the inrush current prevention circuit includes a DC power supply for the inrush current prevention circuit and a current-limiting resistor. The voltage of the DC power supply for the inrush current prevention circuit and the resistance of the current-limiting resistor may be set so that all of the semiconductor switching elements may be turned-on in the range of a given ambient temperature of the inverter device.
According to a sixth aspect of the invention, the plurality of semiconductor switching elements of the inrush current prevention circuit are connected in parallel to each other and the DC power supply for the inrush current prevention circuit is provided in the driving circuit for the inrush current prevention circuit.
According to a seventh aspect of the invention, the plurality of semiconductor switching elements of the inrush current prevention circuit are connected in parallel to each other, and the driving circuit for the inrush current prevention circuit includes a DC power supply for the inrush current prevention circuit and a current-limiting resistor so that the DC power supply for the inrush current prevention circuit may be connected to a trigger terminal of the semiconductor switching element through the current-limiting resistor.
According to an eighth aspect of the invention, the DC power supply for the inrush current prevention circuit is connected to the trigger terminals of the semiconductor switching elements through the current limiting resistors.
According to a ninth aspect of the invention, the DC power supply for the inrush current prevention circuit is connected to the trigger terminal through the photo thyristor.
According to a tenth aspect of the invention, a motor driving device includes a motor, an inverter device, and a control device, the inverter device including a smoothing circuit for smoothing a power supply for a main circuit, an inrush current prevention circuit for preventing inrush current from flowing into the smoothing circuit when the power supply for the main circuit is turned on, and an inverter section for receiving the current from the smoothing circuit for driving the motor, the inrush current prevention circuit including a current-limiter for limiting the inrush current, a plurality of semiconductor switching elements, and a driving circuit for the inrush current prevention circuit for driving these semiconductor switching elements, the semiconductor switching elements of the inrush current prevention circuit being connected in parallel with each other, the driving circuit for the inrush current prevention circuit including a DC power supply for the inrush current prevention circuit and a current-limiting resistor, the DC power supply for the inrush current prevention circuit being connected to the trigger terminal of the semiconductor switching element through the current limiting resistor, and the control device serving to control the inverter section and the driving circuit for the inrush current prevention circuit.